The W-PAL coding and decoding system (also known as Weston Clean PAL) is described in GB 15343268, GB1534269 and GB1534270 and in BBC Research Department Report 1980/1 February 1980 all of which are incorporated herein by reference. It is a form of "clean PAL" which uses comb-filters and modulation of the luminance at a frequency of twice sub-carrier (2fsc), to reduce cross talk between the luminance and chrominance signals.
All W-PAL systems, proposed, contain a band-pass filter which limits the action of the comb filter to the sub-carrier band (approx. 3.3 to 5.5 MHz) for system I PAL. Cross Talk is completely eliminated at all frequencies within this band, where the band-pass filter has unity gain, and also at all frequencies outside the band, where the filter has zero gain. But some cross talk remains in the transition band, where the response is neither unity nor zero.